JP-2002-323351A describes a housing which is mounted to outside of a vehicle. The housing defines a first space and a second space inside, and has an air hole which makes the first space and the second space to communicate with each other. The air hole is covered with a sheet made of a waterproof and breathable material. If water enters the air hole, the air hole is closed by the water film caused by the surface tension. At this time, ventilation function of the air hole does not work.
In JP-2002-323351A, a ventilating passage extending to the air hole is made to have a labyrinth (maze) structure, thereby restricting water from entering the air hole.
However, because the size of the maze structure becomes large, the size of the housing also becomes large, and it becomes difficult to mount the housing. Further, it is difficult to discharge the water if the water reaches the air hole through the maze structure.